Apparatus for testing earth formations composed of particles of various sizes

ABSTRACT

In the representative embodiment of the new and improved apparatus disclosed herein for testing earth formations of differing compositions, fluid-admitting means are selectively extended into sealing engagement with a potentially-producible earth formation. Upon placement of the fluid-admitting means into communication with the isolated formation, a selectivelyadjustable filter of a unique design cooperates therewith so that the typically-large particles of mudcake from the isolated formation wall will pass through the filter without plugging the fluid-admitting means. Should, however, loose formation materials begin entering the fluid-admitting means as the testing is conducted, the filter is responsively adjusted so as to retain these typically-smaller materials and halt their further erosion from the formation wall thereby assuring continued communication with the isolated formation.

Urbanosky Dec, 9, 1975 APPARATUS FOR TESTING EARTH FORMATIONS COMPOSED OF PARTICLES OF VARIOUS SIZES Harold J. Urbanosky, Pearland, Tex.

Schlumberger Technology Corporation, New York, NY.

Filed: Oct. 18, 1973 Appl. No.: 407,736

Published under the Trial Voluntary Protest Program on January 28, 1975 as document no. B 407,736.

Inventor:

Assignee:

US. Cl. 73/155 Int. Cl. E21B 49/00 Field of Search 73/155, 151, 421 R;

References Cited UNITED STATES PATENTS 6/1966 Briggs, Jr. .1 73/155 7/l972 Hallmark 73/155 Primary ExaminerJerry W. Myracle Attorney, Agent, or FirmErnest R. Archambeau, Jr.; William R. Sherman; Stewart F. Moore [57] ABSTRACT In the representative embodiment of the new and improved apparatus disclosed herein for testing earth formations of differing compositions, fluid-admitting means are selectively extended into sealing engagement with a potentially-producible earth formation. Upon placement of the fluid-admitting means into communication with the isolated formation, a selectively-adjustable filter of a unique design cooperates therewith so that the typically-large particles of mudcake from the isolated formation wall will pass through the filter without plugging the fluid-admitting means. Should, however, loose formation materials begin entering the fluid-admitting means as the testing is conducted, the filter is responsively adjusted soas to retain these typically-smaller materials and halt their further erosion from the formation wall thereby assuring continued communication with the isolated formation.

29 Claims, 11 Drawing Figures POWER SUPPLY U.S. Patent D60. 9 1975 Sheet 1 of 7 POWER SUPPLY RECORDER Sheet 3 of 7 3,924,463

USO Patent Dec; 9 1975 U.S. Patent Dec.91975 Shet4of7 3,924,463

F/G.4 I l Patent Dec. 9 1975 Sheet of 7 US. Patent Dec. 9 1975 Sheet 7 of7 3,924,463

APPARATUS FOR TESTING EARTH FORMATIONS 'COMPOSED OF PARTICLES VARIOUS SIZES Until very recently, the so-called wireline formation testers which have been most successful in commercial service have, for the large part, been limited to attempting only a single test or, at best, two tests of selected earth formations penetrated by a given well bore. Generally, the success of these tests has depended to some extent upon knowing in advance the general character of the particular formations which were to be tested so that the tester could be equipped as required to test a formation of a given nature.

For example, where the formations to be tested were considered to be fairly competent and, therefore, not easily eroded, prior-art testers such as that shown in US. Pat. No. 3,011,554 have been highly effective. On the other hand, in those situations where tests were to be conducted in fairly incompetent or unconsolidated formations, it has heretofore been the practice to use new and improved testers such as those shown in US. Pat. Nos. 3,352,361; 3,530,933; 3,565,169; or 3,653,436. As fully described in these last-mentioned patents, each of those prior-art testing tools employs a tubular sampling member which is cooperatively associated with a conventional filter having fluid openings of a selected, but uniform, size for preventing the unwanted entrance of unconsolidated formation materials of a specified minimum size into the testing tool. Thus, except for dual-purpose tools such as that shown in US. Pat. No. 3,261,402, these prior-art formation-testing tools have been most successful in making tests in formations which are known in advance either to be fairly competent or to be relatively unconsolidated. Moreover, since all of these prior-art testers can be operated only once during a single trip into a well bore, it has been customary to simply select in advance the particular size or type of filter believed to be best suited for a specific testing operation.

One of the most significant advances in the formation-testing art, however, has been the'recent introduction into commercial service of the new and improved repetitively-operable testers such as fully described in US. Pat. No. 3,780,575. As disclosed there, these tools are capable of repetitively taking any number of pressure measurements from various formations as well as collecting at least two fluid samples during a single trip into a given well bore.

Nevertheless, although these new and improved testers have been quite successful, there are often situations where the performance of these testers is significantly affected since there has heretofore been no one conventional filtering medium capable of operating efficiently with every type of earth formation. For in stance, if one of these testers must be equipped with a conventional filter which is capable of stopping exceptionally-fine formation matenals, the flow rate for this tester will be materially limited even when a fairlycompetent formation is being tested. More importantly, in situations like this, it is not at all uncommon for the necessarily-fine openings in a conventional filter to be quickly plugged by the normally-large particles of mudcake which usually line the borehole wall adjacent to a potentially-producible formation. Thus, a test under these conditions will often be inconclusive, if not misleading, since it will not be known for sure whether the formation is truly unproductive or if the filter was simply plugged at the outset of the test. On the other hand, where the tester is instead equipped with a con ventional filter having openings designed for filtering out only fairly-large particles, there will often be an excessive induction of very-fine formation materials into the tool when the tool is testing a highly-unconsolidated formation. This action will, of course, frequently result in a continued erosion of the formation wall around the sealing pad so that isolated communication with the formation is quickly lost. This also causes an incomplete or inconclusive test.

It will be recognized, of course, that is wholly impractical to change the filter in a repetitively-operable tool of this type between tests of different types of formations in a given borehole. Moreover, there is no assurance that the character of various potentially-product ble formations traversed by a given borehole can even be reliably determined in advance.

Accordingly, it is an object of the present invention to provide new and improved formation-testing apparatus for reliably obtaining multiple measurements of one or more fluid or formation characteristics as well as for selectively collecting one or more samples of connate fluids, if desired, from different earth formations of any character even where these formations vary in their compositions and competency.

This and other objects of the present invention are attained by providing formation-testin g apparatus having new and improved fluid-admitting means adapted for selective movement into sealing engagement with a potentially-producible earth formation to isolate a portion thereof from the borehole fluids. The fluid-admitting means are provided with filtering means having first and second cooperatively-associated filter members adapted for movement relative to one another and respectively provided with one or more filter passages that are each sized to easily pass large plugging materials such as mudcake particles. Biasing means are cooperatively arranged for normally positioning the filter members so as to partially misalign the associated pairs of their respective filter openings in relation to one another. When the fluid-admitting means are initially placed into communication with an isolated earth formation the filter members are moved to a position where the filter openings are in registration with one another so that mudcake lining the formation wall will readily pass through the fully-registered filter passages thereby leaving the inlet of the filtering means free of such plugging materials. Thereafter, should loose formation materials be inducted into the fluid-admitting means, the biasing means are operative for responsively shifting the filter members toward their normal position where their respective filter openings are partially misaligned so as to reduce the overall effective flow area through each associated pair of filter openings for substantially blocking significant passage of loose formation materials through the effectively-narrowed filter passages without unduly limiting the flow of producible connate fluids through the filtering means.

The novel features of the present invention are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by way of the following description of a preferred embodiment of new and improved apparatus employing the principles of the invention as illustrated in the accompanying drawings, in which:

FIG. 1 depicts the surface and downhole portions of one embodiment of formation-testing apparatus including new and improved fluid-admitting means incorporating the principles of the present invention;

FIG. 2 is an enlarged view of a preferred embodiment of the new and improved fluid-admitting means shown in FIG. 1;

FIGS. 3A and 33 together show a somewhatschematic representation of the formation-testing tool illustrated in FIG. 1 as the tool will appear in its initial operating position;

FIGS. 4, 5, 6A and 6B respectively depict the successive positions of various components of the testing tool shown in FIGS. 3A and 3B during the course of a typical testing and sampling operation to illustrate in general the operation of the new and improved fluidadmitting means of the present invention; and

FIGS. 7-9 schematically illustrate in detail the operation of the new and improved fluid-admitting means of the present invention with different types of earth formations.

Turning now to FIG. 1, a preferred embodiment of new and improved fluid-admitting means 10 incorporating the principles of the present invention is shown on a formation-testing tool 11 as this tool will appear during the course of a typical measuring and sampling operation in a well bore such as a borehole l2 penetrating one or more earth formations as at 13 and 14. As illustrated, the tool 11 is suspended in the borehole 12 from the lower end of a typical multiconductor cable 15 that is spooled in the usual fashion on a suitable winch (not shown) at the surface and coupled to the surface portion of a tool-control system 16 as well as typical recording-and-indicating apparatus 17 and a power supply 18. In its preferred embodiment, the tool 11 includes an elongated body 19 which encloses the downhole portion of the tool-control system 16 and carries a selectively-extendible tool-anchoring member 20 supported by one or more piston actuators, as at 21, on the opposite side of the body from the new and improved fluid-admitting means 10 as well as one or more fluid-collecting chambers 22 and 23 which are tandemly coupled to the lower end of the tool body.

As is explained in greater detail in US. Pat. No. 3,780,575, and which is incorporated by reference herein, the depicted formation-testing tool 11 and its control system 16 are cooperatively arranged so that, upon command from the surface, the tool can be selectively placed in any one or more of five selected operating positions. As will be subsequently described briefly, the control system 16 will function either to successively place the tool 11 in one or more of these positions or else to selectively cycle the tool between various ones of these operating positions. These five operating positions are simply achieved by selectively moving suitable control switches, as schematically represented at 24 and 25, included in the surface portion of the control system 16 to various switching positions, as at 26-31, so as to selectively apply power to different conductors 32-38 in the cable 15.

The new and improved fluid-admitting means 10 of the present invention are cooperatively arranged for selectively sealing-off or isolating selected positions of the wall of the borehole l2; and, once a selected portion of the borehole wall is packed-off or isolated from the borehole fluids, establishing pressure or fluid communication with the adjacent earth formation, as at 13. In the preferred embodiment depicted in FIG. 2, the

fluid-admitting means 10 include an elastomeric annular sealing pad 39 mounted on the forward face of an upright support member or plate 40 that is coupled to a longitudinally-spaced pair of laterally-movable piston actuators, as at 41, which are similar to the actuators 21 and are arranged transversely on the tool body 19 for moving the sealing pad back and forth in relation to the forward side of the tool body. Accordingly, as the control system 16 selectively supplies a pressured hydraulic fluid to the piston actuators 41, the sealing pad 39 will be moved laterally between a retracted position adjacent to the forward side of the tool body 19 and an advanced or forwardly-extended position.

By arranging the annular sealing member 39 on the opposite side of the tool body 19 from the tool-anchoring member 20 (FIG. 1), the simultaneous extension of these two wall-engaging members will, of course, be effective for urging the sealing pad into sealing engagement with the adjacent wall of the borehole 12 as well as for anchoring the tool 11. It should, however, be appreciated that the tool-anchoring member 20 would not be needed if the effective Stroke of the piston actuators 41 is sufficient for assuring that the sealing pad 39 can be extended into firm sealing engagement with one wall of the borehole 12 with the rear of the tool body 19 securely anchored against the opposite wall of the borehole. Conversely, the piston actuators 41 could be similarly omitted where the extension of the toolanchoring member 20 alone would be effective for moving the front side of the tool body 19 forwardly toward one wall of the borehole 12 so as to place the sealing pad 39 into firm sealing engagement therewith. However, it is preferred that both the tool-anchoring member 20 and the fluid-admitting means 10 are arranged to be simultaneously extended to enable the tool 11 to be operated in boreholes of substantial diameter. This preferred design of the tool 11, of course, keeps the overall stroke of the piston actuators 21 and 41 to a minimum so as to reduce the overall diameter of the tool body 19.

To conduct connate fluids into the testing tool 11, the preferred embodiment of the new and improved fluid-admitting means 10 depicted in FIG. 2 further includes a tubular fluid-admitting member 42 having an open forward portion coaxially disposed within the annular sealing pad 39 and a closed rear portion which is slidably mounted within a larger tubular member 43 secured to the rear face of the pad-support plate 40 and extended rearwardly therefrom. As will subsequently be described in greater detail, the new and improved fluid-admitting means 10 further include selectivelyvariable filtering means 44 cooperatively arranged on the forward portion of the fluid-admitting member 42 for selectively straining potentially-plugging materials of differing particle sizes from connate fluids entering the nose of the fluid-admitting member. In the illustrated preferred embodiment of the filtering means 44, the objects of the present invention are best accomplished by coaxially disposing a telescoped pair of tubular filter members 45 and 46 in the forward portion of the fluid-admitting member so as to cover an inwardlyopening annular chamber 47 formed in the member 42. For reasons which will subsequently be explained, the outer filter member 46 is secured, as by threads 48, to the fluid-admitting member 42 and the inner filter member 45 is cooperatively arranged for axial movement between the slightly-extended position illustrated in FIG. 2' and a more-retracted position. Biasing means,

such as one or more springs or Bellville washers 49, are cooperatively arranged between the outwardlyenlarged nose of the inner tube 45 and the nose of the fluid-admitting member 42 for normally maintaining the inner filtering member in its depicted extended position. The significance of this unique arrangement of the filtering means 44 will subsequently be explained.

By arranging the nose of the tubular fluid-admitting member to normally protrude a short distance ahead of the forward face of the sealing pad 39, extension of the fluid-admitting means will engage the forward ends of the fluid-admitting member 42 and the inner filter member 45 with the adjacent surface of the wall of the borehole 12 just before the annular sealing pad is also forced thereagainst for isolating that portion of the borehole wall as well as the noses of the two tubular members from the borehole fluids. The significance of this sequence of engagement will be subsequently explained.

To selectively move the tubular fluid-admitting member 42 in relation to the enlarged outer member 43, the smaller tubular member is slidably disposed within the outer tubular member and fluidly sealed in relation thereto as by sealing members 50 and 51 and on inwardly-enlarged end portions 52 and 53 of the outer member and a sealing member 54 on an enlarged-diameter intermediate portion 55 of the inner member. Accordingly, it will be appreciated that by virtue of the sealing members 50, 51 and 54, enclosed piston chambers 56 and 57 are defined within the outer tubular member 43 and on opposite sides of the outwardlyenlarged portion 55 of the inner tubular member 42 which, of course, functions as a piston member. Thus, by applying an increased hydraulic pressure in the rearward chamber 56, the fluid-admitting member 42 will be moved forwardly in relation to the outer tubular member 43 as well as to the sealing pad 39. Conversely, upon the application of an increased hydraulic pressure to the forward piston chamber 57, the fluid-admitting member 42 will be retracted in relation to the outer member 43 and the sealing pad 39.

Pressure or fluid communication with the new an improved fluid-admitting means 10 of the present invention is preferably controlled by means such as a generally-cylindrical valve member 58 which is coaxially disposed within the fluid-admitting member 42 and the inner filter member 45 and cooperatively arranged for axial movement therein between a retracted or open position and the advanced or closed position depicted in FIG. 2 where the enlarged forward end of the valve member is substantially, if not altogether, sealingly engaged with the forwardmost interior portion of the inner filter member. To support the valve member 58, the rearward portion of the valve member is axially hollowed, as at 59, and coaxially disposed over a tubular member 60 projecting forwardly from the transverse wall 61 closing the rear end of the fluid-admitting member 42. The axial bore 59 is reduced and extended forwardly along the valve member 58 to a termination with one or more transverse fluid passages 62 in the forward portion of the valve member just behind its enlarged head.

To provide actuating means for selectively moving the valve member 58 in relation to the fluid-admitting member 42, the rearward portion of the valve member is enlarged, as at 63, and outer and inner sealing members 64 and 65 are coaxially disposed thereon and respectively sealingly engaged with the interior of the fluid-admitting member and the exterior of the forwardly-extending tubular member 60. A sealing member 66 mounted around the intermediate portion of the valve member 58 and sealingly engaged with the interior wall of the adjacent portion of the fluid-admitting member 42 fluidly seals the valve member in relation to the fluid-admitting member. Accordingly, it will be appreciated that by increasing the hydrualic pressure in the enlarged piston chamber 67 defined to the rear of the enlarged valve portion 63 which serves as a piston member, the valve member 58 will be moved forwardly in relation to the fluid-admitting member 42. Conversely, upon application of an increased hydraulic pressure to the forward piston chamber 68 defined between the sealing members 64 and 66, the valve member 58 will be moved rearwardly along the forwardlyprojecting tubular member 60 so as to retract the valve member in relation to the fluid-admitting member 42 and the inner filter member 45.

Accordingly, when the valve member 58 is retracted from its extended position inside of the filtering means 44, formation fluids will be compelled to pass through the exposed forward portions of the two filter members 45 and 46 ahead of the enlarged head of the valve member, into the annular space 47, and then through a fluid passage 69 in the fluid-admitting member 42 into the fluid passage 62 and the tubular member 60. Thus, as the valve member 58 is retracted, should loose formation materials enter the fluid-admitting means 10, the plugging materials will be stopped by the uniquelyarranged filter means 44 ahead of the enlarged head of the valve member thereby quickly forming a permeable barrier to prevent the continued erosion of loose formation materials once the valve member halts.

Turning now to FIGS. 3A and 3B, the fluid-admitting means 10 as well as the entire downhole portion of the control system 11, the tool-anchoring member 20, and the fluid-collecting chambers 22 and 23 are schematically illustrated with their several elements or components depicted as they will respectively be arranged when the tool 11 is fully retracted and the control switches 24 and 25 are in their first or off operating positions 26 (FIG. 1). Since the aforementioned US. Pat. No. 3,780,575 fully describes the control system 16 and various components of the tool 11, it is believed adequate to simply cover only the major aspects of this system.

A sample or flow line 70 is cooperatively arranged in the formation-testing tool 11 and has one end coupled, as by a flexible conduit 71, to the fluid-admitting means 10 and its other end terminated in a pair of branch conduits 72 and 73 respectively coupled to the fluid-collecting chambers 22 and 23. To control fluid communication between the new and improved fluid-admitting means 10 and the fluid-collecting chambers 22 and 23, normally-closed flow-control valves 74-76 of a similar or identical design are arranged respectively in the flow line 70 and in the branch conduits 72 and 73 leading to the sample chambers. For reasons which will subsequently be described, a normally-open control valve 77 which is preferably similar to the normally-closedcontrol valves 74-76 is cooperatively arranged in a branch conduit 78 for selectively controlling communication between the borehole fluids exterior of the tool 11 and the upper portion of the flow line 70 and the flexible conduit 71 extending between the flow-line control valve 74 and the new and improved fluid-admitting means 10.

As illustrated, the normally-open control valve 77, for example, is operated by a typical pressure-responsive actuator 79 which is arranged to close the valve in response to an actuating pressure of at least a predetermined magnitude. As fully described in the aforementioned US. Pat. No. 3,780,575, a spring biasing the control valve 77 to its open position is cooperatively arranged to establish the magnitude of the pressure required to close the valve. Furthermore, the normallyclosed control valves 74-76 are preferably similar to the control valve 77 except that they are respectively operated by pressure-responsive actuators 80-82 selectively arranged to open these valves in response to pressures of different predetermined magnitudes.

In the particular embodiment of the testing tool 11 shown in FIGS. 3A and 3B, a branch conduit 83 is coupled to the flow line 70 at a convenient location between the sample-chamber control valves 75 and 76 and the flow-line control valve 74, with this branch conduit being terminated at an expansion chamber 84 of a predetermined volume. A reduced-diameter displacement piston 85 is operatively mounted in the chamber 84 and arranged to be moved between selected upper and lower positions therein by a typical piston actuator shown generally at 86. Accordingly, it will be appreciated that upon movement of the displacement piston 85 from its lower position as illustrated in FIG. 3A to an elevated or upper position, the combined volume of whatever fluids that are then contained in the branch conduit 83 as well as in that portion of the flow line 70 between the flow-line control valve 74 and the sample-chamber control valves 75 and 76 will be correspondingly increased.

As best seen in FIG. 3A, the control system 16 further includes a pump 87 that is coupled to a driving motor 88 and cooperatively arranged for pumping a suitable hydrualic fluid such as oil or the like from a reservoir 89 into a discharge or outlet line 90. Since the tool 11 is to be operated at-extreme depths in boreholes, as at 12, which typically contain dirty and usually corrosive fluids, the reservoir 89 is preferably arranged to totally immerse the pump 87 and the motor 88 in the clean hydraulic fluid. The reservoir 89 is also provided with a spring-biased isolating piston 91 for maintaining the hydraulic fluid at a pressure about equal to the hydrostatic pressure at whatever depth the tool is then situated as well as accommodating volumetric changes in the hydraulic fluid which may occur under different borehole conditions. One or more inlets, as at 92 and 93, are provided for returning hydraulic fluid from the control system 16 to the reservoir 89 during the operation of the tool 11.

The fluid outlet line 90 is divided into two major branch lines which are respectively designated as at set line 94 and the retract line 95. To control the admission of hydraulic fluid to the set and retract lines 94 and 95, a pair of normally-closed solenoid-actuated valves 96 and 97 are cooperatively arranged to selectively admit hydraulic fluid to the two lines as the control switch 24 at the surface is selectively positioned;

and a typical check valve 98 is arranged in the set line 94 downstream of the control valve 96 for preventing the reverse flow of the hydraulic fluid whenever the pressure in the set line is greater than that then existing in the fluid outlet line 90. Typical pressure switches 99-101 are cooperatively arranged in the set and retract lines 94 and 95 for selectively starting and stopping the pump 87 as required to maintain the line pressure within a selected operating range. Since the pump 87 is preferably a positive-displacement type to achieve a rapid predictable rise in the operating pressures in the set and retract lines 94 and 95, each time the pump is to be started the control system 16 also functions to temporarily open the control valve 97 (if it is not already open) as well as a third normally-closed solenoidactuated valve 102 for bypassing hydraulic fluid directly from the output line to the reservoir 89 by way of the return line 92. Once the motor 88 has reached operating speed, the bypass valve 102 will, of course, be reclosed and either the set line control valve 96 or the retract line control valve 97 will be selectively opened as required for that particular operational phase of the tool 11.

Accordingly, it will be appreciated that the control system 16 cooperates for selectively supplying pressured hydraulic fluid to the set and retract lines 94 and 95. Since the pressure switches 99 and respectively function only to limit the pressures in the set and retract lines to a selected maximum pressure range com mensurate with the rating of the pump 89, the control system 16 is further arranged to cooperatively regulate the pressure of the hydraulic fluid which is being supplied at various times to selected protions of the system. Although this regulation can be accomplished in different manners, it is preferred to employ a number of pressure-actuated control valves such as those shown schematically at 103-106 in FIGS. 3A and 3B for controlling the hydraulic fluid in the control system 16. As shown in FIG. 3A, the hydraulic control valve 103, for example, includes a valve body 107 having an enlarged upper portion carrying a downwardly-biased actuating piston 108-which is cooperatively coupled to a valve member 109 as by an upright stem 110 thereon which is slidably disposed in an axial bore 111 in the piston. A spring 112 of selected strength is disposed in the axial bore 111 for normally urging the valve member 109 into seating engagement.

In its non-actuated position depicted in FIG. 3A, the hydraulic control valve 103 (as well as the valve 104) will, therefore, simply function as a normally-closed check valve. That is to say, in this operating position, hydraulic fluid can flow only in a reverse direction whenever the pressure at the valve outlet is sufficiently greater than the inlet pressure to unseat the valve member 109 against the predetermined closing force imposed by the spring 112. On the other hand, whenever the actuating piston 108 is elevated by the application of hydraulic pressure thereto, opposed shoulders, as at 1 13, on the stem 110 and the piston 108 will engage for unseating the valve member 109. As shown in FIGS. 3A and 3B, it will be appreciated that the hydraulic control valve (as well as the valve 106) is similar to the hydraulic control valve 103 except that in these first-mentioned control valves, the valve member, as at 1 14, is preferably rigidly coupled to its associated actuating piston, as at 115. Thus, the hydraulic control valve 105 (as well as the valve 106) has no alternate checking action allowing reverse flow but is simply a normally-closed pressure-actuated valve for selectively controlling fluid communication between its inlet and outlet ports.

The set line 94 downstream of the check valve 98 is comprised of a low-pressure section 116 having one branch 1 17 coupled to the fluid inlet of the hydraulic control valve 105 and another branch 118 which is coupled to the fluid inlet of the hydraulic control valve 103 to selectively supply hydraulic fluid to a high-pressure section 119 of the set line which is itself terminated at the fluid inlet of the hydraulic control valve 106. To regulate the supply of hydraulic fluid from the low-pressure section 116 to the high-pressure section 119 of the set line 94, a pressure-communicating line 120 is coupled between the low-pressure section and the control port of the hydraulic control valve 103. Accordingly, so long as the pressure of the hydraulic fluid in the low-pressure section of the set line 94 remains below the predetermined actuating pressure required to open the hydraulic control valve 103, the high-pressure section 119 will be isolated from the low-pressure section 116. Conversely, once the hydraulic pressure in the low-pressure line 116 reaches the predetermined actuating pressure of the valve 103, the hydraulic con trol valve will open to admit the hydraulic fluid into the high-pressure line 119.

The hydraulic control valves 105 and 106 are respectively arranged to selectively communicate the lowpressure and high-pressure sections 116 and 119 of the set line 94 with the fluid reservoir 89. To accomplish this, the control ports of the two hydraulic control valves 105 and 106 are each connected to the retract line 95 by suitable pressure-communicating lines 121 and 122. Thus, whenever the pressure in the retract line 95 reaches their respective predetermined actuat ing levels, the hydraulic control valves 105 and 106 will be respectively opened to selectively communicate the two sections 116 and 119 of the set line 94 with the reservoir 89 by way of the return line 92 coupled to the respective fluid outlets of the two control valves.

As previously mentioned, in FIGS. 3A and 3B the tool 11 and the sub-surface portion of the control system 16 are depicted as their several components will appear when the tool is retracted. At this point, the tool-anchoring member 20 and the sealing pad 39 are respectively retracted against the tool body 19 to facilitate passage of the tool 11 into the borehole 12. To prepare the tool 11 for lowering the borehole 12, the switches 24 and 25 are moved from their first or off positions 26 to their second or initialization positions 27. At this point, the hydraulic pump 87 is started to raise the pressure in the retract line 95 to a selected maximum to be certain that the pad 39 and the toolanchoring member 20 are fully retracted. At this time, the pressure-equalizing valve 77 is open and that portion of the flow line 70 between the closed flow-line control valve 74 and the fluid-admitting means will be filled with borehole fluids as the tool 1 1 is being lowered into the borehole 12.

When the tool 11 is at a selected operating depth, the switches 24 and 25 are advanced to their third positions 28. Then, once the pump 87 has reached its rated operating speed, the hydraulic pressure in the output line 90 will rapidly rise to its selected maximum operating pressure as determined by the maximum or off setting of the pressure switch 99. As the pressure progressively rises, the control system 16 will successively function at selected intermediate pressure levels for sequentially operating the several control valves 7477 and 103 106 in an operating cycle such as the one described fully in the aforementioned US. Pat. No. 3,780,575. It must, however, be recognized that the forthcoming particular operational sequence of the tool 11 as illustrated is not essential to the successful operation of the new and improved fluid-admitting means 10. Those skilled in the art will, therefore, un-

10 derstand that the present invention can be practiced either with different types of formation-testing tools or with different arrangements of the tool 1 1 and the control system 16.

Turning now to FIG. 4, selected portions of the control system 16 and various components of the tool 11 are schematically represented to illustrate the operation of the illustrated embodiment of the tool at about the time that the pressure in the hydraulic output line reaches its lowermost intermediate pressure level. To facilitate an understanding of the operation of the tool 11 and the control system 16 at this point in its operating cycle illustrated in the several drawings, only those components which are then operating are shown in FIG. 4.

At this time, since the control switch 24 (FIG. 1) is in its third position 28, the solenoid valves 96 and 102 will be open; and, since the hydraulic pressure in the set line 94 has not yet reached the upper pressure limit as determined by the pressure switch 99, the pump motor 88 will still be operating. Since the hydraulic control valve 103 (not shown in FIG. 4) is closed, the high pressure section 119 of the set line 94 will still be iso' lated from the low-pressure section 116. Simultaneously, the hydraulic fluid contained in the forward pressure chambers of the piston actuators 21 and 41 will be displaced (as shown by the arrows as at 123) to the retract line and returned to the reservoir 89 by way of the open solenoid valve 102. These actions will, of course, cause the tool-anchoring member 20 as well as the sealing pad 39 to be respectively extended in op posite lateral directions until each has moved into firm engagement with the opposite sides of the borehole 12.

It will be noticed in FIG. 4 that hydraulic fluid will be admitted by way of branch hydraulic lines 124 and 125 to the enclosed annular chamber 56 to the rear of the enlarged-diameter portion 55 of the fluid-admitting member 42. At the same time, hydraulic fluid from the piston chamber 57 ahead of the enlarged-diameter portion 55 will be discharged by way of branch hydraulic lines 126 and 127 to the retract line 95 for progressively moving the fluid-admitting member forwardly in relation to the sealing member 39 until the noses of the fluid-admitting member 42 and the inner filter member 45 engage the wall of the borehole 12 and then halt. The sealing pad 39 is then urged forwardly in relation to the now-halted tubular member 42 until the pad sealingly engages the borehole wall for packing-off or isolating the isolated wall portion from the borehole fluids. In this manner, mudcake immediately ahead of the fluid-admitting member 42 will be displaced radially away from the nose of the fluid-admitting member so as to minimize the quantity of unwanted mudcake which will subsequently be admitted into the fluidadmitting means 10. Those skilled in the art will appreciate the significance of this unique arrangement.

It should also be noted that although the pressured hydraulic fluid is also admitted at this time into the forward piston chamber 68 between the sealing members 64 and 66 on the valve member 58, the valve member is temporarily prevented from moving rearwardly in relation to the inner and outer tubular members 42 and 60 inasmuch as the hydraulic control valve 104 (not shown in FIG. 4) is preferably still closed thereby temporarily trapping the hydraulic fluid in the rearward piston chamber 67 to the rear of the valve member. The purpose of this delay in the retraction of the valve member 58 will be subsequently explained.

As also illustrated in FIG. 4, the hydraulic fluid in the low-pressure section 116 of the set line 94 will also be directed by way of a branch hydraulic line 128 to the piston actuator 86. This will, of course, result in the displacement piston 85 being elevated as the hydraulic fluid from the piston actuator 86 is returned to the retract line 95 by way of a branch hydraulic conduit 129. As will be appreciated, elevation of the displacement piston 85 in the expansion chamber 84 will be effective for significantly decreasing the pressure initially existing in the isolated portions of the branch line 83 and the flow line 70 between the still-closed flow-line control valve 74 and the still-closed chamber control valves 75 and 76 (not shown in FIG. 4). The purpose of this pressure reduction will be subsequently explained.

Once the tool-anchoring member 20, the sealing pad 39 and the fluid-admitting member 42 have respectively reached their extended positions as illustrated in FIG. 4, it will be appreciated that the hydraulic pressure delivered by the pump 89 will again rise. Then, once the pressure in the output line 90 has reached its second intermediate level of operating pressure, the hydraulic control valve 104 will open in response to this pressure level to now discharge the hydraulic fluid previously trapped in the piston chamber 67 to the rear of the valve member 58 back to the reservoir 89.

As illustrated in FIG. 5, once the hydraulic control valve 104 opens, the hydraulic fluid will be displaced from the rearward piston chamber 67 by way of branch hydraulic lines 130, 131 and 127 to the retract line 95 as pressured hydraulic fluid from the set line 94 surges into the piston chamber 68 ahead of the enlarged-diameter portion 63 of the valve member 58. This will, of course, cooperate to rapidly drive the valve member 58 rearwardly in relation to the now-halted fluid-admitting member 42 for establishing fluid or pressure communication between the isolated portion of the earth formation 13 and the flow passages 62 and 69 in the valve member by way of the filter means 44.

Although this is not fully illustrated in FIG. 5, it will be recalled from FIGS. 3A and 3B that the control valves 74-76 are initially closed to isolate the lower portion of the flow line 70 between these valves as well as the branch line 83 leading to the pressure-reduction chamber 84. However, the flow-line pressure-equalizing control valve 77 will still be open at the time the hydraulic control valve 104 opens to retract the valve member 58 as depicted in FIG. 5. Thus, as the valve member 58 progressively uncovers the new and improved filtering means 44, borehole fluids at a pressure greater than that of the connate fluids which may be present in the isolated earth formation 13 will be introduced into the upper portion of the flow line 70 and, by way of the flexible conduit member 71, into the rearward end of the tubular member 60. As these highpressure borehole fluids pass into the annular space 47 around the filtering means 44, they will be forcibly discharged (as shown by the arrows 132) from the forward end of the fluid-admitting member 42 for washing away any plugging materials such as mudcake or the like which may have become deposited on the internal surface of the filtering member 45 when it is first uncovered by the retraction of the valve member 58. Thus, the particular embodiment of the control system 16 illustrated in the drawings is operative for providing a momentary outward surge or reverse flow of borehole fluids for cleansing the filtering means 44 of unwanted debris or the like before a sampling or testing operation 12 is commenced. This is, however, not essential to the successful operation of the new and improved fluidadmitting means 10.

It will be appreciated that once the several components of the formation-testing tool 11 and the control system 16 have reached their respective positions as depicted in FIG. 5, the hydraulic pressure in the output line 94 will again quickly increase to its next intermediate pressure level. Once the pump 87 has increased the hydraulic pressure in the output line 90 to this next predetermined intermediate pressure level, the hydraulic control valve 103 will selectively open as depicted in FIG. 6A. As seen there, opening of the hydraulic control valve 103 will be effective for now supplying hydraulic fluid to the high-pressure section 119 of the set line 94 and two branch conduits 133 and 134 connected thereto for successively closing the pressureequalizing control valve 77 and then opening the flowline control valve 74.

In this manner, as respectively depicted by the several arrows at 135 and 136, hydraulic fluid at a pressure representative of the intermediate operating level will be supplied by way of a typical check valve 137 to the upper portion of the actuator 79 of the normally-open pressure equalizing valve 77 as fluid is exhausted from the lower portion of the actuator by way of a conduit 138 coupled to the retract line 95. This will, of course, be effective for closing the pressure-equalizing valve 77 so as to now block further communication between the flow line 70 and the borehole fluids exterior of the tool 1 1. Simultaneously, the hydraulic fluid will also be admitted to the lower portion of the actuator 80 of the flow-line control valve 74. By arranging the actuator 79 for the normally-open pressure-equalizing valve 77 to operate somewhat quicker than the actuator 80 for the normally-closed flow-line control valve 74, the second valve will be momentarily retained in its closed position until the first valve has had time to close. Then, once the pressure-equalizing valve 77 closes, as the hydraulic fluid enters the lower portion of the actuator 80 of the flow-line control valve 74, the latter valve will be opened as hydraulic fluid is exhausted from the upper portion of its actuator through a typical check valve 139 and a branch return line 140 coupled to the retract line 95.

It will be appreciated, therefore, that with the tool 11 in the position depicted in FIGS. 6A and 6B, the flow line 70 is now isolated from the fluids in the borehole 12 and is in communication (by way of the flexible conduit 71) with that portion of the formation 13 isolated by the sealing pad 39. As will subsequently be explained, the tool 11 is now in readiness to obtain one or more pressure measurements as well as samples of any producible connate fluids in the formation 13.

Before continuing further with a description of a typical testing operation with the tool 11, it is believed appropriate to now consider the unique operation of the new and improved fluid-admitting means 10 of the present invention at this point in the testing operation. However, the significance of the present invention will be best understood when the performance of prior-art formation testers with conventional filters is first understood. Typically, these prior-art formation testers have simply used elongated tubular filters having only a plurality of narrow slits of a uniform width which are disposed either longitudinally along the tubular member or circumferentially around the member. US. Pat. No. 3,352,361 is an example of this previous practice.

Alternatively, the fluid-sampling member in these prior-art testers has been fitted with either a porous member or a finely-meshed screen of a conventional design such as described, for example, in U.S. Pat. No. 3,653,436' In any case, these prior-art tools have employed conventional filters having only uniformly-sized filter openings which are customarily sized as dictated by the particular size of formation particles which were expected to be encountered during a given testing operation.

It has been found, however, that when these prior-art filters are used in soft formations, the pressure drop across the filtering element and the accumulated formation particles will often become so excessive that a fluid sample simply cannot be obtained in a reasonable period of time. This is easily understood when a priorart testing tool such as shown in US. Pat. No. 3,653,436 is considered. As shown in FIG. of that patent, fluids entering the nose of the sampling tube will be divided along a number of fluid paths, with the shortest path being through the first opening in the filter screen at the forward end of the sampling tube and the longest path theoretically being through the sampling tube and out the rearwardmost opening in the screen. In actuality, however, it has been found that by virtue of the additional flow resistance imposed by the tightly-packed column of finely-divided sand particles and mudcake which will be quickly trapped in the sampling tube, most, if not all, of the flow will be through the forwardmost openings in the filter screen. Thus, since at best, little or none of the flow will be through the rearward portions of the screen, the overall flow rate will be drastically curtailed. It should be noted in passing, however, that in this situation, it is unlikely that the filter screen will be entirely plugged by mudcake since any mudcake initially entering the sampling tube is typically concentrated in the rearward end of the tube and held there by the collected column of sand since the mudcake particles are ordinarily too large to pass through filter openings small enough to retain the sand particles. Experience has shown, however, that if the screen openings are slightly oversized so that some sand grains will pass through the front openings, it is not at all uncommonn for the sand to gradually erode the filter screen to the point that the screen is no longer effective. Thus, enlargement of the openings to improve the flow rate will often result in rapid failure of the filter.

A more-serious problem is encountered, however, when a prior-art testing tool equipped with a conventional filter having very narrow slits is used to test a fairly competent or hard formation. In this situation, the usual result will be that the mudcake entering the sampling tube will swirl around inside of the tube so that the internal or inlet face of the filter screen will be quickly coated with the mudcake particles thereby plugging most, if not all, of the narrow filter openings. I-Ieretofore, the only practical solution to this problem has been to use a screen with the largest-possible openings that will hopefully still trap any loose formation materials which might be encountered. This obviously poses a problem where formations composed of different degrees of hardness or competency are expected to be encountered during a multi-formation testing operation such as is capable of being performed by the tool 11. Thus, if the filter openings are too large, sand will easily pass through the filter screen when unconsolidated formations are tested. On the other hand, if the screen openings are too small, they will be easily plugged by mudcake when hard formations are tested.

The new and improved fluid-admitting means 10 of the present invention avoids these several problems, however. Accordingly, as best seen in FIGS. 7 and 8, somewhat-simplified enlarged views are respectively shown of the new and improved fluid-admitting means 10 at successive moments during the initiation of a test of an incompetent earth formation, as at 13, which is primarily composed of extremely-fine particles of sand and the like. At the time illustrated in FIG. 7, the various elements of the tool 11 have just been placed in their respective positions as previously described by reference to FIGS. 6A and 6B. As illustrated in FIG. 7, the inner and outer filter tubes 45 and 46 are respectively slitted, as at 141 and 142, so as to provide a plurality of circumferentialIy-oriented slits which are preferably arranged in sets or rows of two or three slits around the tubes and distributed at uniform intervals substantially along the full length of each tube. Each of the slits, as at 141 and 142, is of a selected width which itself has been found suitable for normally passing large particles of mudcake with little risk of plugging. In one embodiment of the new and improved filtering means 44, it was found that a width of about 0.018-inch for each of the several slits, as at 141 and 142, was quite successful.

It will be noted, therefore, in FIG. 7 that when the inner and outer filter members 45 and 46 are shifted to their illustrated fully-telescoped or retracted position (as permitted by a movement-limiting arrangement such a lateral pin 143 and longitudinally-elongated slot 144), the slits 141 will be fully registered with the slits 142 so as to selectively provide maximum-sized fluid openings through the filtering means 44. On the other hand, as illustrated in FIGS. 2 and 8, in the normal extended position of the telescoped filter members 45 and 46, the biasing springs 49 will be effective for moving the slits 141 nearly out of registration with the slits 142 so that the net effective width of each associated pair of the slits will be substantially less than their full individual width. For example, in the aforementioned embodiment of the filtering means 44, it was found to be quite successful to arrange the stop pin 143 and its receiving slot 144 for halting the filter members 45 and 46 when the effective flow opening through each associated pair of the slits was in the order of only 0.006- inch. Thus, with this particular embodiment of the new and improved filtering means 44, the effective flow opening through each associated pair of the slits 141 and 142 is at a minimum of about 0.006-inch when the filtering members 45 and 46 are extended and at a maximum of about 0.018-inch when the filtering members are fully-telescoped or retracted. It will be recognized, however, that by virtue of the biasing springs 49, the filter members 45 and 46 will normally be in their fullyextended position so as to ordinarily minimize the net effective flow openings through associated pairs of the slits 141 and 142 to a selected sand-trapping width.

As previously discussed, when the fluid-admitting means 10 are first extended against a formation,.as at 13, there will be a plug of mudcake, as at 145 in FIG. 7, on the wall of the borehole 12 which will be isolated by the sealing pad 39. Accordingly, to assure that the mudcake plug 145 will not block the filtering means 44 when the valve member 58 first opens communication between the formation 13 and the flow line 70, the spring means 49 are cooperatively selected to respond to the initial engagement of the inner filter tube 45 against the wall of the borehole 12 so as to at least temporarily force this tube back into the outer tube 46 as far as permitted by the lug 143 and the slot 144. It should be noted that even highly-unconsolidated formations are typically sufficiently compacted by the borehole hydrostatic pressure as to initially require a substantial force on the fluid-admitting member 42 and the filter member 45 before the borehole wall is penetrated. Thus, even assuming that the formation 13 is relatively incompetent, the rearward movement of the valve member 58 through the inner filtering member 45 will initially induct the plug of mudcake 145 into the nose of the fluid-admitting member 42 ahead of whatever loose formation materials, as at 146, that may immediately flow into the forwardly-moving fluid-admitting member. Since the fluid-admitting member 42 can advance into the formation 13 only by correspondingly displacing loose formation materials, as at 146, into the fluid-admitting member, it will be appreciated that so long as the fluid-admitting member is moving forwardly the nose of the inner filter tube 45 will encounter sufficient opposition to still overcome the biasing spring 49 and thereby maintain the slits 141 and 142 in full registration. Thus, at least a substantial portion of the mudcake plug 145 will have the opportunity of escaping through the fully-opened slits 141 and 142.

Once, however, the fluid-admitting member 42 reaches its fully-extended position shown in FIG. 8, the nose of the inner filtering tube 45 will no longer be meeting sufficient resistance to overcome the biasing springs 49. Thus, as illustrated, the biasing springs 49 will cooperate for selectively returning the filtering members 45 and 46 to their fully-extended position so as to again locate the slits 141 and 142 in relation to one another so that the net effective flow opening of each associated pair of slits is at a minimum. This will, of course, serve to cooperatively collect the entering loose formation particles 146'for now providing a permeable barrier or compacted column of the clean sand particles to halt the further entry of loose sand particles into the fluid-admitting means 10. It should be recognized that once the filtering means 44 operates to stop the flow of additional sand particles into the fluidadmitting means 10, there can be no further erosion of the isolated portion of the wall of the borehole 12 since there is now no place for such additional particles to go.

It will be appreciated, therefore, that when a relatively-incompetent formation, as at 13, is to be tested, the filtering means 44 will cooperate to initially shift the filtering members 45 and 46 to their retracted position for locating the associated pairs of the slits 141 and 142 so as to provide a maximum flow opening to pass at least most of the incoming mudcake plug 145 on downstream of the filtering means. Then, as sand particles, as at 146, flow into the filtering means 44, the biasing means 49 will cooperate to return the filtering members 45 and 46 to their respective extended positions for relocating the associated pairs of the slits 141 and 142 so as to provide a minimum flow opening for effectively collecting the clean sand particles into a compacted column or permeable barrier just ahead of the valve member 58 which is sufficient to halt further entry of additional sand particles.

On the other hand, as shown in FIG. 9, should the formation interval 14 being tested be relatively wellcompacted, the advancement of the fluid-admitting member 42 will be relatively slight with its nose making little or no penetration into the earth formation. It will, of course, be appreciated that the fluid-admitting means 10 will be urged outwardly with sufficient force for the noses of the fluid-admitting member 42 and the inner filter member 45 to at least penetrate the mudcake 147 which typically lines the walls of the borehole 12 adjacent to permeable formations, as at 14. Thus, in this situation, the inner filter member will be immediately urged against the wall of the borehole 12 with sufficient force for shifting the filter members 45 and 46 to their retracted positions so as to allow the incoming mudcake particles 148 to readily pass on through the fully-open pairs of associated slits 141 and 142.

In contrast, however, to the situation just described with respect to incompetent formations, as at 13, the engagement of the inner filter member against the competent formation 14 shown in FIG. 9 will instead result in the filter members 45 and 46 remaining in their fullyretracted position so as to leave the associated pairs of the slits 141 and 142 fully open. Thus, as the valve member 58 moves to its depicted rearward position, all mudcake, as at 148, entering the fluid-admitting means 10 will be free to pass easily through the new and improved filtering means 44 without blocking subsequent communication with the formation 14.

Accordingly, it will be appreciated that regardless of the nature'of the formation, as at either 13 or 14, which is encountered during a testing operation by the formation-testing tool 11, mudcake, as at 148, which enters the fluid-admitting member 42 at the very outset of the testing operation is capable of freely passing through the fully-registered slits 141 and 142 and on into the flow line 70. Therefore, as shown in both FIGS. 7 and 9, by virtue of the new and improved apparatus of the present invention mudcake particles, as at 148, are effectively purged from the interiors of the fluid-admitting member 42 and the filtering members 45 and 46 so as to promptly eliminate this as a subsequent source of possibly-plugging materials. It should be noted that even should a competent formation, as at 14, begin to slough for some reason, the filtering means 44 nevertheless has the capability of shifting the filtering slits 141 and 142 to a narrow position as necessary to accommodate any change in formation conditions.

As best seen in FIGS. 6A and 6B, therefore, should there be any producible connate fluids in the isolated earth formation 13 (or the formation 14), the formation pressure will be effective for displacing these connate fluids by way of the new and improved fluidadmitting means 10 into the flow line until such time that the lower portion of the flow line and the branch conduit 83 are filled and pressure equilibrium is established in the entire flow line. By arranging a typical pressure-measuring transducer, as at 149 (or, if desired, one or more other suitable types of propertymeasuring transducers) in the flow line 70, one or more measurements representative of the characteristics of the connate fluids and the formation 13 may be transmitted to the surface by a conductor 149a and either indicated or, if desired, recorded on the recording apparatus 17 (FIG. 1.). In any event, the pressure measurements provided by the transducer 149 will, of course, permit the operator at the surface to readily determine the formation pressure as well as to obtain one or more indications representative of the potential producing capability of the formation 13 (or the formation 14). The various techniques for analyzing formation pressures are well known in the art and are, therefore, of no significance to understanding the present invention.

The measurements provided by the pressure transducer 149 at this time will indicate whether the sealing pad 39 has, in fact, established complete sealing engagement with the earth formation 13 (or the formation 14) inasmuch as the expected formation pressures will be recognizably lower than the hydrostatic pressure of the borehole fluids at the particular depth which the tool 11 is then situated. This ability to determine the effectiveness of the sealing engagement will, of course, allow the operator to retract the tool-anchoring member 20 and the sealing pad 39 without having to unwittingly or needlessly continue the remainder of the complete operating sequence.

Assuming, however, that the pressure measurements provided by the pressure transducer 149 show that the sealing pad 39 is firmly seated, the operator may leave the formation-testing tool 11 in the position shown in FIGS. 6A and 68 as long as it is desired to observe as well as to record the pressure measurements. As a result, the operator can determine such things as the time required for the formation pressure to reach equilibrium as well as the rate of any pressure increase and thereby obtain valuable information indicative of various characteristics of the earth formation 13 such as permeability and porosity. Moreover, with the illustrated embodiment of the tool 11, the operator can readily determine if collection of a fluid sample is warranted.

Referring again to FIGS. 6A and 6B, it will be appreciated that once the several components of the tool 11 and the control system 16 have moved to their respective positions shown in these figures, the hydraulic pressure will again rise until such time that the set line pressure switch 99 operates to halt the hydraulic pump 87. Inasmuch as the pressure switch 99 has a selected operating range, in the typical situation the pump 87 will be halted shortly after the pressure-equalizing valve 77 closes and the flow-line control valve 74 opens. At this point in the operating cycle of the tool 11, once a sufficient number of pressure measurements have been obtained, a decision can be made whether it is advisable to obtain one or more samples of the producible connate fluids present in the earth formation 13, If such samples are not desired, the operator can simply operate the control switches 24 and 25 for re tracting the tool-anchoring member 20 well as the sealing pad 39 without further ado. This freedom of action is, of course, made possible by virtue of the flexibility of operation of the new and improved fluid-admitting means and the assurance that connate fluids can reliably pass through the filter means 44.

On the other hand, should a fluid sample be desired, the control switches 24 and 25 (FIG. 1) are advanced to their next or so-called sample positions 29 to open, for example, a solenoid valve 150 (FIG. 318) for coupling pressured hydraulic fluid from the high-pressure section 119 of the set line 94 to the piston actuator 81 of the sample-chamber control valve 75. This will, of course, be effective for opening the chamber control valve 75 to admit connate fluids through the flow line 70 and the branch conduit 72 into the sample chamber 22. If desired, a chamber selection switch 151 (FIG. 1) in the surface portion of the control system 16 could also be moved from its first sample position 152 to its so-called second sample position 153 (FIG. 1) to energize a solenoid valve 154 (FIG. 3B) for opening the other sample-chamber control valve 76 to also admit connate fluids into the second sample chamber 23. In either case, one or more samples of the connate fluids which are present in the isolated earth formation 13 (or the formation 14) can be selectively obtained by the testing tool 11.

Upon moving the control switches 24 and 25 to their so-called sample-trapping positions 30, the pump 87 will again be restarted. Once the pump 87 has reached operating speed, it will commence to operate much in the same manner as previously described and the hydraulic pressure in the output line 90 will again begin rising with momentary halts at various intermediate pressure levels.

Accordingly, when the control switches 24 and 25 have been placed in their sample-trapping positions 30 (FIG. 1), the solenoid valve 97 (FIGS. 3A and 3B) will open to admit hydraulic fluid into the retract line 95. By means of the electrical conductor 101a, however, the pressure switch 101 is enabled and the pressure switch 100 is disabled so that in this position of the control switches 24 and 25 the maximum operating pressure which the pump 87 can initially reach is limited to the pressure at the operating pressure level determined by the pressure switch 101. Thus, by arranging the hydraulic control valve 106 to open in response to a hydraulic pressure corresponding to this predetermined pressure level, hydraulic fluid in the high-pressure section 119 of the set line 94 will be returned to the reservoir 89 by means of the return line 92. As the hydraulic fluid in the high-pressure section 119 returns to the reservoir 89, the pressure in this portion of the set line 94 will be rapidly decreased to close the hydraulic control valve 103 once the pressure in the line is insufficient to hold the valve open. Once the hydraulic control valve 103 closes, the pressure remaining in the low-pressure section 116 of the set line 94 will remain at a reduced pressure which is nevertheless effective for retaining the tool-anchoring member 20 and the sealing pad 39 fully extended.

As hydraulic fluid is discharged from the lower portion of the piston actuator 81 by way of the still-open solenoid-valve 150 and fluid from the retract line enters the upper portion of the actuator by way of a branch line 155, the sample-chamber control valve 75 will close to trap the sample of connate fluids which is then present in the sample chamber 22. Similarly, should a fluid sample have also been collected in the second sample chamber 23, the other sample-chamber control valve 76 can also be readily closed by operating the switch 151 (FIG. 1) to reopen the solenoid valve 154. Closure of the sample-chamber control valve 75 (as well as the valve 76) will, of course, be effective for trapping any fluid samples collected in one or the other or both of the sample chambers 22 and 23.

Once the sample-chamber control valve 75 (and, if necessary, the control valve 76) has been reclosed, the control switches 24 and 25 are moved to their next or so-called retracted switching positions 31 for initiating the simultaneous retraction of the tool-anchoring member 20 and the sealing pad 39. In this final position of the control switch 25, the pressure switch 101 is again rendered inoperative and the pressure switch is enabled so as to now permit the hydraulic pump 87 to be operated at full rated capacity for attaining hydraulic pressures greater than the first intermediate operating level in the retract cycle. Once the pressure switch 101 19 has again been disabled, the pressure switch 100 will now function to operate the pump 87 so that the pressure will now quickly rise until it reaches the next operating level.

At this point, hydraulic fluid will be supplied through the retract line 95 and the branch hydraulic line 138 for reopening the pressure-equalizing control valve 77 to readmit borehole fluids into the flow line 70. Opening of the pressure-equalizing valve 77 will admit borehole fluids into the isolated space defined by the sealing pad 39 so as to equalize the pressure differential existing across the pad before it is retracted. Hydraulic fluid displaced from the upper portion of the piston actuator 79 of the pressure-equalizing valve 77 will be discharged through a typical relief valve 156 which is arranged to open only in response to pressures equal or greater than that of this present operating level. The hydraulic fluid displaced from the piston actuator 79 through the relief valve 156 will be returned to the reservoir 89 by way of the branch hydraulic line 133, the high-pressure section 119 of the set line 94, the still-open hydraulic control valve 106, and the return line 92.

When the hydraulic pressure in the output line 90 has either reached the next operating level or, if desired, a still-higher level, pressured hydraulic fluid in the retract line 95 will reopen the hydraulic control valve 105 to communicate the low-pressure section 1 16 of the set line 94 with the reservoir 89. When this occurs, hydraulic fluid in the retract line will be admitted to the retract sides of the several piston actuators 21 and 41. Similarly, the pressured hydraulic fluid will also be admitted into the annular space 57 in front of the enlarged-diameter piston portion 55 for retracting the fluid-admitting member 42 as well as into the annular space 67 for returning the valve member 58 to its forward position. The hydraulic fluid exhausted from the several piston actuators 21 and 41 as well as the piston chambers 56 and 68 will be returned directly to the reservoir 89 by way of the low-pressure section 116 of the set line 94 and the hydraulic control valve 105. This action will, of course, retract the tool-anchoring member 20 as well as the sealing pad 39 against the tool body 19 to permit the tool 11 either to be repositioned in the borehole 12 or to be returned to the surface if no further testing is desired.

It should be noted that although there is an operating pressure applied to the upper portion of the piston actuator 80 for the flow-line control valve 74 at the time that the pressure-equalizing valve 77 is reopened, a normally-closed relief valve 157 which is paralleled with the check valve 139 is held in a closed position until the increasing hydraulic pressure developed by the pump 87 exceeds the operating level used to retract the tool-anchoring member 20 and the sealing pad 39. At this point, in the operating sequence of the new and improved tool 11, the flow-line control valve 74 will be reclosed.

The pump 87 will, of course, continue to operate until such time that the hydraulic pressure in the output line 90 reaches the upper limit determined by the setting of the pressure switch 99. At some convenient time thereafter, the control switches 24 and 25 are again returned to their initial or off positions 26 for halting further operation of the pump motor 88 as well as reopening the solenoid valve 102 to again communicate the retract line 95 with the fluid reservoir 89. This completes the operating cycle of the illustrated embodiment of the tool 11.

Accordingly, it will be appreciated that the new and improved fluid-admitting means 10 of the present invention enable the formation-testing tool, such as that shown herein at 11, to be operated for testing any type of formation which may be reasonably expected to be encountered during a formation-testing operation. By providing filter means with selectively-adjustable filter openings, it is assured that a buildup of formation particles in the sampling member will not block the flow of connate fluids through the fluid-admitting means. Thus, with the new and improved filtering means described herein, tests may now be conducted in various types of formations without experiencing either unduly-reduced flow rates where a given formation is composed of exceptionally-fine sand particles or having the testing tool plugged by mudcake or the like.

While only a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. Formation-testing apparatus adapted for suspension in a borehole having mudcake lining the walls thereof adjacent to earth formations containing producible connate fluids and comprising:

a body having a fluid passage adapted to receive connate fluids; fluid-admitting means on said body including a fluid entry adapted to be engaged with a borehole wall for isolating a surface thereof from borehole fluids;

means selectively operable for positioning said fluidadmitting meansagainst a borehole wall to place said fluid entry into communication with earth formations beyond an isolated borehole wall surface; and

selectively-positionable fluid-filtering means cooperatively arranged in fluid communication between said fluid passage and said fluid entry and operatively movable upon engagement of said fluidadmitting means with an isolated borehole wall surface to one filtering position for initially passing mudcake particles displaced from an isolated borehole wall surface on through said filtering means into said fluid passage and operatively movable toward another filtering position whenever loose formation particles are eroded from an isolated borehole wall surface for collecting such loosened formation particles in said fluid entry as connate fluids pass on through said filtering means into said fluid passage.

2. The formation-testing apparatus of claim 1 wherein said fluid-filtering means include:

first and second filtering members respectively provided with first and second filter openings and cooperatively arranged for movement relative to one another between said one filtering position wherein said filter openings mutually define at least one enlarged filter passage sufficient to pass enlarged mudcake particles and said other filtering position wherein said filter openings mutually define at least one reduced filter passage sufficient to retain loose formation particles.

3. The formation-testing apparatus of claim 2 wherein said first and second filter openings are all at least substantially the same size.

21 4. The formation-testing apparatus of claim 2 wherein said first and second filter openings are elongated slits at least substantially the same size.

5. The formation-testing apparatus of claim 1 wherein said fluid-filtering means include:

first and second filtering members respectively provided with first and second filter openings and cooperatively arranged for movement relative to one another between said one filtering position wherein said filter openings are at least substantially aligned with one another to mutually define at least one enlarged filter passage sufficient to pass enlarged mudcake particles and said other filtering position wherein said filter openings are at least partially misaligned with one another to mutually define at least one reduced filter passage sufficient to retain loose formation particles.

6. The formation-testing apparatus of claim 5- wherein said first and second filter openings are all at least substantially the same size.

7. The formation-testing apparatus of claim 5 wherein said first and second filter openings are elongated slits at least substantially the same size.

8. The formation-testing apparatus of claim 1 wherein said fluid-filtering means include:

first and second filtering members respectively provided with a plurality of filter openings and cooperatively arranged within said fluid-admitting means to the rear of said fluid entry for longitudinal movement of said first filtering member relative to said second filtering member between said one filtering position wherein each associated pair of said filter openings in said filtering members mutually define an enlarged filter passage sufficient to pass enlarged mudcake particles and said other filtering position wherein each associated pair of said filter openings in said filtering members mutually define a reduced filter passage sufficient to retain loose formation particles;

first means coupled to said first filtering member and adapted to engage an isolated borehole wall surface for shifting said first filtering member to said one filtering position upon engagement of said fluid-admitting means with an isolated borehole wall surface; and

second means coupled to said first filtering member and adapted for shifting said first filtering member to said other filtering position upon disengagement of said first means from an isolated borehole wall surface.

9. The formation-testing apparatus of claim 8 further including:

means selectively operable after disengagement of said fluid-admitting means from an isolated borehole wall surface for displacing from said fluid entry any loosened formation particles previously collected in said fluid entry.

10. The formation-testing apparatus of claim 8 further including:

pressure-measuring means coupled to said fluid passage and adapted for providing at least one measurement representative of the pressure of connate fluids in said fluid passage.

11. The formation-testing apparatus of claim 8 further including:

sample-collecting means on said body and selectively operable for obtaining a sample of connate fluids in said fluid passage.

12. The formation-testing apparatus of claim 8 further including:

pressure-measuring means coupled to said fluid passage and adapted for providing at least one measurement representative of the pressure of connate fluids in said fluid passage; and

sample-collecting means on said body and selectively operable for obtaining a sample of connate fluids in said fluid passage.

13. The formation-testing apparatus of claim 12 further including:

means selectively operable after disengagement of said fluid-admitting means from an isolated borehole wall surface for displacing from said fluid entry any loosened formation particles previously collected in said fluid entry.

14. Formation-testing apparatus adapted for suspension in a borehole having mudcake lining the walls thereof adjacent to earth formations containing producible connate fluids and comprising:

a body having a fluid passage adapted to receive confluid-admitting means on said body and including a fluid-sampling member having a tubular inlet passage adapted to be engaged with a borehole wall for isolating a surface thereof from borehole fluids and an outlet passage downstream of said inlet passage and coupled to said fluid passage, and means on said fluid-sampling member defining a chamber upstream of said outlet passage and adapted for collecting loose formation particles entering said inlet passage;

means selectively operable for positioning said fluidsampling member against a borehole wall to place said inlet passage into communication with earth formations therebeyond; and

filtering means on said fluid-sampling member for intercommunicating said inlet and outlet passages and including first and second filtering members respectively having first and second filter openings each selectively sized to pass mudcake particles and cooperatively arranged between said inlet and outlet passages for sliding movement of said first filtering member across said second filtering member between a first position wherein said first and secondfilter openings mutually define a corresponding number of enlarged filtering passages sufficient to pass enlarged mudcake particles and a second position wherein said first and second filter openings mutually define a corresponding number of reduced filtering passages sufficient to retain loose formation particles, means cooperatively arranged between said filtering members for respectively defining said first and second positions, first actuating means cooperatively arranged for shifting said first filtering member to said first position in response to engagement of said fluid-admitting means with a borehole wall to allow mudcake particles displaced therefrom into said fluid-sampling member to pass readily through said enlarged filtering passages into said outlet passage, and second actuating means cooperatively arranged for shifting said first filtering member to said second position in response to displacement of loose formation particles into said fluid-sampling member from a borehole wall engaged thereby.

15. The formation-testing apparatus of claim 14 further including:

pressure-measuring means coupled to said fluid pas-.

sage and adapted for providing at least one measurement representative of the pressure of connate fluids in said fluid passage.

16. The formation-testing apparatus of claim 14 further including:

sample-collecting means on said body and selectively operable for obtaining a sample of connate fluids in said fluid passage.

17. The formation-testing apparatus of claim 14 further including:

pressure-measuring means coupled to said fluid passage and adapted for providing at least one measurement representative of the pressure of connate fluids in said fluid passage; and

sample-collecting means on said body and selectively operable for obtaining a sample of connate fluids in said fluid passage.

18. The formation-testing apparatus of claim 14 further including:

a piston member coaxially arranged in said fluid-sampling member for movement between a retracted position in a rearward portion thereof to close off the rear of said particle-collecting chamber and an extended position in a forward portion of said fluidsampling member; and

means coupled to said piston member and selectively operable for moving said piston member to its said retracted position following engagement of said fluid-admitting means with a borehole wall to admit connate fluids into said fluid-sampling member and for moving said piston member to its extended position following disengagement of said fluid-admitting means from a borehole wall to displace any loosened formation materials previously collected in said particle-collecting chamber from said fluid-sampling member.

19. Formation-testing apparatus adapted for suspension in a borehole having mudcake lining the walls thereof adjacent to earth formations containing producible connate fluids and comprising:

a body having a fluid passage adapted to receive confluid-admitting means on said body and including a fluid-sampling member having a tubular forward portion defining an inlet passage adapted to be engaged with a borehole wall for isolating a surface thereof from borehole fluids, and an outlet passage coupled to said fluid passage and having an inwardly-facing entrance in said tubular forward portion downstream of said inlet passage;

means selectively operable for positioning said fluidsampling member against a borehole wall to establish communication with earth formations therebeyond;

filtering means between said inlet and outlet passages adapted for limiting the entrance of loose formation particles into said fluid passage and including a fixed filtering member having a plurality of filter openings covering said outlet passage entrance, a movable filtering member having a plurality of filter openings complementally fitted over said fixed filtering member and adapted for movement relative thereto between one position where said filter openings in each of said filtering members mutually define a corresponding number of enlarged filtering passages sufficient to pass mudcake particles and another position where said filter openings in 24 each of said filtering members mutually define a corresponding number of reduced filtering passages sufficient to retain loose formation particles, first means cooperatively arranged on said fluidsampling member and operable for moving said movable filtering member toward its said one position upon engagement of said fluid-sampling member with a borehole wall'to allow mudcake particles displaced therefrom into said fluid-sampling member to pass readily through said enlarged filtering passages into said outlet passage, and second means cooperatively arranged on said fluid-sampling member for moving said movable filtering member toward its said other position in response to displacement of loose formation materials into said fluid-sampling member from a borehole wall engaged thereby; and means adapted for controlling the entrance of particles into said fluid-sampling member and including a piston member coaxially arranged in said fluidsampling member for movement past said filtering members between an advanced position within said tubular forward portion ahead of said filter openings blocking communication into said fluid-sampling member and a retracted position to the rear of said filter openings for uncovering said filtering members and defining a space to the rear thereof for collecting loosened formation particles entering said tubular forward portion, and piston-control means cooperatively arranged for selectively moving said piston member back and forth between its said advanced and retracted positions.

20. The formation-testing apparatus of claim 19 wherein said outlet passage entrance is defined by an annular chamber formed around an interior wall portion of said fluid-sampling member between said advanced and retracted positions of said piston member; and said filtering members are respectively tubular members coaxially mounted in said fluid-sampling member around said annular chamber with said movable filter member being sized for passage of said piston member as it moves between its said positions.

21. The fonnation-testing apparatus of claim 19 wherein said filter openings are respectively comprised of a plurality of circumferentially-oriented slits spaced longitudinally along each of said filter members with the width of each of said slits being selectively sized for passage of mudcake particles, and wherein the movement of said movable filtering member is longitudinally in relation to said fluid-sampling member.

22. The formation-testing apparatus of claim 21 wherein the distance between said positions of said movable filtering member is selected so that each of said slits in said movable filtering member is always cooperatively associated with the same one of said slits in said fixed filtering member.

23. The formation-testing apparatus of claim 19 further including:

sealing means cooperatively arranged on said fluidadmitting means around said tubular forward portion and adapted for packing-off a borehole wall around said tubular forward portion.

24. The formation-testing apparatus of claim 19 further including:

means cooperatively mounting said fluid-sampling member on said body for movement relative thereto between a laterally-extended position and a retracted position; and 

1. Formation-testing apparatus adapted for suspension in a borehole having mudcake lining the walls thereof adjacent to earth formations containing producible connate fluids and comprising: a body having a fluid passage adapted to receive connate fluids; fluid-admitting means on said body including a fluid entry adapted to be engaged with a borehole wall for isolating a surface thereof from borehole fluids; means selectively operable for positioning said fluid-admitting means against a borehole wall to place said fluid entry into communication with earth formations beyond an isolated borehole wall surface; and selectively-positionable fluid-filtering means cooperatively arranged in fluid communication between said fluid passage and said fluid entry and operatively movable upon engagement of said fluid-admitting means with an isolated borehole wall surface to one filtering position for initially passing mudcake particles displaced from an isolated borehole waLl surface on through said filtering means into said fluid passage and operatively movable toward another filtering position whenever loose formation particles are eroded from an isolated borehole wall surface for collecting such loosened formation particles in said fluid entry as connate fluids pass on through said filtering means into said fluid passage.
 2. The formation-testing apparatus of claim 1 wherein said fluid-filtering means include: first and second filtering members respectively provided with first and second filter openings and cooperatively arranged for movement relative to one another between said one filtering position wherein said filter openings mutually define at least one enlarged filter passage sufficient to pass enlarged mudcake particles and said other filtering position wherein said filter openings mutually define at least one reduced filter passage sufficient to retain loose formation particles.
 3. The formation-testing apparatus of claim 2 wherein said first and second filter openings are all at least substantially the same size.
 4. The formation-testing apparatus of claim 2 wherein said first and second filter openings are elongated slits at least substantially the same size.
 5. The formation-testing apparatus of claim 1 wherein said fluid-filtering means include: first and second filtering members respectively provided with first and second filter openings and cooperatively arranged for movement relative to one another between said one filtering position wherein said filter openings are at least substantially aligned with one another to mutually define at least one enlarged filter passage sufficient to pass enlarged mudcake particles and said other filtering position wherein said filter openings are at least partially misaligned with one another to mutually define at least one reduced filter passage sufficient to retain loose formation particles.
 6. The formation-testing apparatus of claim 5 wherein said first and second filter openings are all at least substantially the same size.
 7. The formation-testing apparatus of claim 5 wherein said first and second filter openings are elongated slits at least substantially the same size.
 8. The formation-testing apparatus of claim 1 wherein said fluid-filtering means include: first and second filtering members respectively provided with a plurality of filter openings and cooperatively arranged within said fluid-admitting means to the rear of said fluid entry for longitudinal movement of said first filtering member relative to said second filtering member between said one filtering position wherein each associated pair of said filter openings in said filtering members mutually define an enlarged filter passage sufficient to pass enlarged mudcake particles and said other filtering position wherein each associated pair of said filter openings in said filtering members mutually define a reduced filter passage sufficient to retain loose formation particles; first means coupled to said first filtering member and adapted to engage an isolated borehole wall surface for shifting said first filtering member to said one filtering position upon engagement of said fluid-admitting means with an isolated borehole wall surface; and second means coupled to said first filtering member and adapted for shifting said first filtering member to said other filtering position upon disengagement of said first means from an isolated borehole wall surface.
 9. The formation-testing apparatus of claim 8 further including: means selectively operable after disengagement of said fluid-admitting means from an isolated borehole wall surface for displacing from said fluid entry any loosened formation particles previously collected in said fluid entry.
 10. The formation-testing apparatus of claim 8 further including: pressure-measuring means coupled to said fluid passage and adapted for providing at least one measurement representative of the pressure of connate fluids in sAid fluid passage.
 11. The formation-testing apparatus of claim 8 further including: sample-collecting means on said body and selectively operable for obtaining a sample of connate fluids in said fluid passage.
 12. The formation-testing apparatus of claim 8 further including: pressure-measuring means coupled to said fluid passage and adapted for providing at least one measurement representative of the pressure of connate fluids in said fluid passage; and sample-collecting means on said body and selectively operable for obtaining a sample of connate fluids in said fluid passage.
 13. The formation-testing apparatus of claim 12 further including: means selectively operable after disengagement of said fluid-admitting means from an isolated borehole wall surface for displacing from said fluid entry any loosened formation particles previously collected in said fluid entry.
 14. Formation-testing apparatus adapted for suspension in a borehole having mudcake lining the walls thereof adjacent to earth formations containing producible connate fluids and comprising: a body having a fluid passage adapted to receive connate fluids; fluid-admitting means on said body and including a fluid-sampling member having a tubular inlet passage adapted to be engaged with a borehole wall for isolating a surface thereof from borehole fluids and an outlet passage downstream of said inlet passage and coupled to said fluid passage, and means on said fluid-sampling member defining a chamber upstream of said outlet passage and adapted for collecting loose formation particles entering said inlet passage; means selectively operable for positioning said fluid-sampling member against a borehole wall to place said inlet passage into communication with earth formations therebeyond; and filtering means on said fluid-sampling member for intercommunicating said inlet and outlet passages and including first and second filtering members respectively having first and second filter openings each selectively sized to pass mudcake particles and cooperatively arranged between said inlet and outlet passages for sliding movement of said first filtering member across said second filtering member between a first position wherein said first and second filter openings mutually define a corresponding number of enlarged filtering passages sufficient to pass enlarged mudcake particles and a second position wherein said first and second filter openings mutually define a corresponding number of reduced filtering passages sufficient to retain loose formation particles, means cooperatively arranged between said filtering members for respectively defining said first and second positions, first actuating means cooperatively arranged for shifting said first filtering member to said first position in response to engagement of said fluid-admitting means with a borehole wall to allow mudcake particles displaced therefrom into said fluid-sampling member to pass readily through said enlarged filtering passages into said outlet passage, and second actuating means cooperatively arranged for shifting said first filtering member to said second position in response to displacement of loose formation particles into said fluid-sampling member from a borehole wall engaged thereby.
 15. The formation-testing apparatus of claim 14 further including: pressure-measuring means coupled to said fluid passage and adapted for providing at least one measurement representative of the pressure of connate fluids in said fluid passage.
 16. The formation-testing apparatus of claim 14 further including: sample-collecting means on said body and selectively operable for obtaining a sample of connate fluids in said fluid passage.
 17. The formation-testing apparatus of claim 14 further including: pressure-measuring means coupled to said fluid passage and adapted for providing at least one measurement representative of the pressure of connate fluids in said fluid passage; and sample-coLlecting means on said body and selectively operable for obtaining a sample of connate fluids in said fluid passage.
 18. The formation-testing apparatus of claim 14 further including: a piston member coaxially arranged in said fluid-sampling member for movement between a retracted position in a rearward portion thereof to close off the rear of said particle-collecting chamber and an extended position in a forward portion of said fluid-sampling member; and means coupled to said piston member and selectively operable for moving said piston member to its said retracted position following engagement of said fluid-admitting means with a borehole wall to admit connate fluids into said fluid-sampling member and for moving said piston member to its extended position following disengagement of said fluid-admitting means from a borehole wall to displace any loosened formation materials previously collected in said particle-collecting chamber from said fluid-sampling member.
 19. Formation-testing apparatus adapted for suspension in a borehole having mudcake lining the walls thereof adjacent to earth formations containing producible connate fluids and comprising: a body having a fluid passage adapted to receive connate fluids; fluid-admitting means on said body and including a fluid-sampling member having a tubular forward portion defining an inlet passage adapted to be engaged with a borehole wall for isolating a surface thereof from borehole fluids, and an outlet passage coupled to said fluid passage and having an inwardly-facing entrance in said tubular forward portion downstream of said inlet passage; means selectively operable for positioning said fluid-sampling member against a borehole wall to establish communication with earth formations therebeyond; filtering means between said inlet and outlet passages adapted for limiting the entrance of loose formation particles into said fluid passage and including a fixed filtering member having a plurality of filter openings covering said outlet passage entrance, a movable filtering member having a plurality of filter openings complementally fitted over said fixed filtering member and adapted for movement relative thereto between one position where said filter openings in each of said filtering members mutually define a corresponding number of enlarged filtering passages sufficient to pass mudcake particles and another position where said filter openings in each of said filtering members mutually define a corresponding number of reduced filtering passages sufficient to retain loose formation particles, first means cooperatively arranged on said fluid-sampling member and operable for moving said movable filtering member toward its said one position upon engagement of said fluid-sampling member with a borehole wall to allow mudcake particles displaced therefrom into said fluid-sampling member to pass readily through said enlarged filtering passages into said outlet passage, and second means cooperatively arranged on said fluid-sampling member for moving said movable filtering member toward its said other position in response to displacement of loose formation materials into said fluid-sampling member from a borehole wall engaged thereby; and means adapted for controlling the entrance of particles into said fluid-sampling member and including a piston member coaxially arranged in said fluid-sampling member for movement past said filtering members between an advanced position within said tubular forward portion ahead of said filter openings blocking communication into said fluid-sampling member and a retracted position to the rear of said filter openings for uncovering said filtering members and defining a space to the rear thereof for collecting loosened formation particles entering said tubular forward portion, and piston-control means cooperatively arranged for selectively moving said piston member back and forth between its said advanced and retracted positions.
 20. The formation-testing apparatUs of claim 19 wherein said outlet passage entrance is defined by an annular chamber formed around an interior wall portion of said fluid-sampling member between said advanced and retracted positions of said piston member; and said filtering members are respectively tubular members coaxially mounted in said fluid-sampling member around said annular chamber with said movable filter member being sized for passage of said piston member as it moves between its said positions.
 21. The formation-testing apparatus of claim 19 wherein said filter openings are respectively comprised of a plurality of circumferentially-oriented slits spaced longitudinally along each of said filter members with the width of each of said slits being selectively sized for passage of mudcake particles, and wherein the movement of said movable filtering member is longitudinally in relation to said fluid-sampling member.
 22. The formation-testing apparatus of claim 21 wherein the distance between said positions of said movable filtering member is selected so that each of said slits in said movable filtering member is always cooperatively associated with the same one of said slits in said fixed filtering member.
 23. The formation-testing apparatus of claim 19 further including: sealing means cooperatively arranged on said fluid-admitting means around said tubular forward portion and adapted for packing-off a borehole wall around said tubular forward portion.
 24. The formation-testing apparatus of claim 19 further including: means cooperatively mounting said fluid-sampling member on said body for movement relative thereto between a laterally-extended position and a retracted position; and control means cooperatively arranged for selectively moving said fluid-sampling member back and forth between its said extended and retracted positions.
 25. The formation-testing apparatus of claim 19 further including: sample-receiving means on said body and adapted for receiving filtered connate fluids entering said fluid passage; and control means cooperatively arranged for selectively coupling said sample-receiving means to said fluid passage.
 26. The formation-testing apparatus of claim 19 further including: pressure-monitoring means for providing indications at the surface indicative of the pressure of connate fluids in said fluid passage.
 27. The formation-testing apparatus of claim 19 further including: a wall-engaging member movably mounted on said body on the opposite side thereof from said forward portion of said fluid-sampling member; and piston means cooperatively coupled to said wall-engaging member for moving said wall-engaging member between an extended wall-engaging position and a retracted position against said opposite body side to respectively engage and disengage said fluid-admitting means with and from a borehole wall.
 28. The formation-testing apparatus of claim 19 further including: means cooperatively coupling said fluid-sampling chamber to said body for movement relative to one side thereof between a laterally-extended position and a retracted position; and piston means cooperatively coupled to said fluid-sampling member for moving said fluid-sampling member between its said laterally-extended position and its said retracted position to respectively engage and disengage said fluid-sampling member with and from a borehole wall.
 29. The formation-testing apparatus of claim 28 further including: a wall-engaging member movably mounted on said body on the opposite side thereof; and piston means cooperatively coupled to said wall-engaging member for moving said wall-engaging member between an extended wall-engaging position and a retracted position against said opposite body side upon movement of said fluid-sampling member between its said positions. 